The present invention relate to systems for maintaining a desired sealing force in connection with producing packaging materials, and particularly to systems which incorporate a closed loop control system.
One technique for producing packaging materials including bags and pouches has included selectively applying a heated sealing force to multiple layers of unrolled material, where the multiple layers have been selectively bonded together as a result of the applied sealing force. The heat is generally applied under a sealing pressure that causes to be bonded or sealed together select portions of the multiple layers.
One area where such a technique has been used is in the manufacturing of medical pouches. Given the nature of the medical industry and the type of items being packaged, medical pouch manufacturers typically have had more stringent requirements and guidelines than other types of industries having similar packaging processes, which need to be adhered to during the manufacturing of the pouches. Process specifics such as heat and force are examples of processing parameters that have been more tightly controlled in an attempt to ensure a consistent high quality for the pouches produced.
However, heat parameters can change over time, especially throughout a particular job run. Generally, both the heat and the sealing force are applied through a platen. In many instances, at initial start-up, the platen will be hot, but will have an insufficient amount of stored heat energy to handle the fresh, cool material being initially supplied. As the job continues over the course of the run, a heat equilibrium is established. The ambient conditions in and around the machine reach a more stable level and new operating parameters apply. However even after an equilibrium is established, the equilibrium can be subsequently affected, for example by interruptions during the manufacturing run, which can include short stops for lunch, breaks, and/or the like, that can cause the heat characteristics to change.
Other processing parameters can also vary, and thereby effect the specific heat and force, which is applied to the material, and ultimately affect the quality of the pouch being produced. For example, the properties of the material used to form the one or more of the layers of material can vary as the material is unrolled. The properties of the material can also change as new rolls of material are loaded onto the system. The platen itself, as well as the surface against which the platen presses the material, can also add to the variability. As the heated plate seals against a sealing surface, like rubber, the rubber surface begins to wear or form an impression according to the die in use. This can have the effect of changing the sealing characteristics, and more specifically can affect the effective sealing force.
One prior approach used in an attempt to meet the requirements of the medical industry included collecting data of the principal operating parameters, like heat and temperature throughout a packaging run, often indirectly. At the end of the run, a sample from the run would be tested to insure that it met the manufacturing requirements desired, and if so, it would be assumed that the other pouches produced, similarly met the requirements, so long as the parameter measurements could be shown to have been maintained at a consistent level throughout the manufacturing run.
One such prior system incorporated a hydraulic or pneumatic control of the platen. The operator would enter the desired force by adjusting a hydraulic regulator, and the desired valve response times. A computer would then calculate the time that the valve is on, and send signals to open and close the valve. The valve would then send the hydraulic flow to the platen cylinder, and a pressure transducer connected to the fluid pressure in the cylinder would send a voltage output consistent with the fluid pressure measurement to a data collection device. The data would then be reviewed to identify any inconsistencies.
However because of the potential for the operating environment to change, as noted above, the pressure reading from the pressure transducer in the hydraulic cylinder does not always directly correlate to the actual sealing pressure applied to the layers of material. Nor does a consistent reading from the pressure transducer insure that a consistent pressure was applied to the layers of material. Furthermore, in such a system, the data was not fed back or used to adjust the operating characteristics of the system during the run. The data was often only used to chart system performance and attempt to determine consistency after the fact.
Consequently, it would be desirable to more directly measure the desired processing parameters, such as sealing force, and to be able to suitably adjust the operating characteristics during a manufacturing run, in order to maintain the parameters at the desired level.
These and other objects, features, and advantages of this invention are evident from the following description of a preferred embodiment of this invention, with reference to the accompanying drawings.
The present invention provides for a system for maintaining a desired sealing force including a closed loop control system. The system includes a platen, which has a surface for making contact with one or more items to be sealed. The system further includes a motor for producing a linear movement, a linkage coupled to the platen and the motor for transferring the linear movement produced by the motor to the platen, and a transducer coupled between the linkage and the platen for measuring the force applied to the platen via the linkage through the linear movement of the motor and producing a signal representative of the force measured. A motor controller produces a motor control signal, where the motor controller is coupled to the motor for supplying the control signal thereto. The motor control signal is used to control the linear movement produced by the motor. The motor controller further receives the feedback signal from the transducer, and correspondingly adjusts the value of the control signal used to control the magnitude of the linear movement.
In one embodiment of the present invention the transducer is incorporated as part of a pin which couples the platen to the linkage. In at least another embodiment a spring is used as part of the linkage to regulate the force applied as a measure of the linear movement created by the motor.
Other features and advantages of the present invention will be apparent from the following detailed description, the accompanying drawings, and the appended claims.